1. Field of the Invention
The present invention relates to a liquid crystal panel module, and to a liquid crystal display device using the liquid crystal panel module.
2. Description of the Related Art
Most notebook computers and dedicated laptop wordprocessors available today use a liquid crystal display (LCD) device mounted on the inside of a cover for a monitor. Such LCDs typically comprise a transparent liquid crystal panel, a light guide for guiding illumination light to the LC panel, a lamp disposed to one side of the light guide, and a reinforced plastic or metal frame in which these and other components are housed.
In the market for notebook computers in particular, however, demand remains great for ever smaller, lighter, and thinner systems. This has driven demand for thinner LCD devices.
FIG. 9 is a sectional view of a conventional LCD device 100 such as is commonly used in notebook computers. As will be known from the figure, this LCD device 100 has a liquid crystal panel module 102 disposed in a frame 101 with a mask frame 103 affixed to the top.
The liquid crystal panel module 102 comprises, assembled in sequence on a plastic frame 104, a backlight unit 105, stacked films 109 comprising an optical diffusion sheet and a lens sheet, and TFT LC panel unit 110.
The backlight unit 105 comprises a light guide 106 with a reflective sheet affixed to the bottom side thereof as seen in FIG. 9, a reflector 107 with a circular cross section, and a lamp 108.
Metal chassis 11a and 111b for securing the liquid crystal panel module 102 to the frame 101 are provided at the left and right sides of the panel module 102.
Note that U.S. Pat. No. 5,504,605, for example, teaches the construction of a liquid crystal module using a plastic frame.
With a liquid crystal panel module 102 as described above and shown in FIG. 9, there are three major factors limiting the reduction in module thickness. These are described below.
FIG. 10 is a view of the plastic frame 104 in the above-described liquid crystal panel module 102. As shown in FIG. 10, the plastic frame 104 is manufactured with a uniform thickness except for the lamp housing, both to reliably secure components therein, and to ensure sufficient strength in the liquid crystal panel module 102. The thickness of this plastic frame 104 is a first factor limiting thinner liquid crystal panel modules 102.
While making the LCD device 100 thinner, it is still essential to ensure a certain minimum strength. The strength of the LCD device 100, however, is more dependent on the strength of the frame than on the strength of the liquid crystal panel module 102.
This suggests that the liquid crystal panel module 102 could be made thinner by making the plastic frame 104 thinner, thus solving the first problem noted above. Doing so, however, creates a further problem, specifically, reliably securing the TFT LC panel unit 110 to the backlight unit 105 becomes difficult.
Circuits and wiring harnesses for the gate and control signal buses used for controlling the operation of the TFT LC panel unit 110 are also disposed between the plastic frame 104 and light guide 106. A plurality of protrusions are also provided on the top of the plastic frame 104 for supporting the light guide 106.
When the gap between the plastic frame 104 and light guide 106 is narrowed by an external force applied to the plastic frame 104, the light guide 106 is pushed up by one or more protrusions 115 on the plastic frame 104. This causes the light guide 106 to push up on the film 109 and thereby on the TFT LC panel unit 110. This results in display irregularities on the screen of the TFT LC panel unit 110.
To prevent such display irregularities from appearing on the screen of the TFT LC panel unit 110 in a typical liquid crystal panel module 102 as described above, a certain minimum gap is typically maintained between the plastic frame 104 and light guide 106. In addition, this gap also normally has sufficient extra tolerance, and is the second major factor limiting further reduction in the thickness of liquid crystal panel module 102.
It would also seem that the liquid crystal panel module 102 could be made thinner by narrowing the sufficient gap between the plastic frame 104 and light guide 106 to the same thickness as the thickest circuit and protrusion interposed to this gap. In this case, however, small vibrations induced by operating the keyboard, opening and closing the cover, and other operations can cause the circuit and protrusion to contact the light guide 106. Display irregularities can again result easily.
Variations in manufacturing precision can also produce distortion in the light guide 106. A specific gap is therefore provided between the light guide 106 and the TFT LC panel unit 110 in a typical liquid crystal panel module 102 as described above to prevent the distorted part of the light guide 106 from pushing up from below on the TFT LC panel unit 110 and causing display irregularities as described above. This gap is a third major factor limiting further reduction in the thickness of liquid crystal panel module 102. In addition, small contaminants and foreign objects can easily penetrate this gap, resulting in black spots, luminance errors, and other display irregularities.
The liquid crystal panel module 102 can again be made thinner by narrowing this gap, but when there are distortions in the light guide 106 and these distortions are pressed against the TFT LC panel unit 110, display irregularities will still occur.
As described above, it is difficult to resolve the problems associated with the above three factors to reduce the thickness of the thinner liquid crystal panel module 102 with a construction as described above.
A further problem is related to the reflector 107 with a circular section that is used in the backlight unit 105 of a typical liquid crystal panel module 102 as shown in FIG. 12. In this case, the thickness, or more specifically the diameter D as shown in the figure, of the reflector 107 must be reduced to achieve a thinner LCD device. Reducing the diameter D of the reflector 107, however, is complicated by the following problems.
Specifically, when the reflector 107 is made thinner, the diameter of the lamp 108, which is supported on both ends inside the reflector 107, must also be reduced. Reducing the lamp 108 diameter, however, can make it more difficult to precisely position the lamp 108 inside the reflector 107 due to variations in component dimensions and applied force.
Reducing the diameter of the lamp 108 also reduces its rigidity and resistance to loads, including gravity, vibration, and impact, applied perpendicular to the longitudinal axis of the lamp. In addition, vibrations caused by typing on the keyboard can also cause the position of the lamp 108 to shift.
FIG. 13 is a graph showing the relationship between the distance X from the center point A of the reflector 107 to the center point B of the lamp 108, and the incidence efficiency (%) of light from the lamp to the light guide. As will be known from FIG. 13, a slight change in the position of the lamp 108 results in a significant change in the efficiency with which a circular section reflector 107 makes the emitted light incident on the light guide 106.
As will therefore be understood, when a small diameter lamp 108 is used and the distance of the lamp 108 from the center of the reflector 107 is different at the two ends of the lamp, light from the lamp 108 cannot be guided to the light guide 106 with uniform luminance along the entire axial length of the lamp.
Furthermore, even if the lamp 108 is positioned to the reflector 107 with a uniform distance therebetween throughout the entire length of the lamp, variations in this distance to the center of the reflector 107 in different LC panel modules can easily produce variations in the luminance of the light guided to the light guide 106 in different modules.
Yet further, even if the lamp 108 is precisely mounted in a specific position in the reflector 107, typing on the keyboard and other vibrations can cause the position of the lamp 108 to shift as described above. As also described, such slight changes in position can cause a significant change in light incidence to the light guide 106, resulting in inconsistent brightness in the TFT LC panel unit 110.
It should be noted that as the reflector 107 is made thinner, support members 120 and 121 for holding the lamp 109 inside the reflector 107 can be provided as shown in FIG. 14 as a means of fixing the position of the lamp 108 relative to the reflector 107. This, however, creates yet another problem, that is, shadows 123 appearing as indicated by the shaded areas in FIG. 14 at each support member 120 and 121.